1. Field of the Invention
The present invention relates generally to automatic controls for vacuum cleaners and more specifically to automatic motor control shutoff systems designed to respond to clogged conditions present anywhere in the dirty air passageway or filter of a vacuum cleaner of the clean air variety and further responsive to the presence and proper placement of the filter as a prerequisite to motor operation.
2. History of the Invention
Automatic arrangements for signaling the operator when the dust bag or filter of a vacuum cleaner has become clogged are well known in the art and reference to U.S. Pat. No. 2,230,113 will enable an appreciation of a typical arrangement utilized in conventional upright vacuum cleaners of several decades ago. Such an automatic arrangement is found in the context of an upright cleaner which operates on "dirty air" principles; that is a system wherein a nozzle inlet is provided in a base or lower housing of the cleaner and the fan for providing suitable suction is likewise contained in such housing and the outlet of the fan forces the air into a filter bag or receptacle. In such a system, the variation in the back pressure of air due to the increased obstruction when the bag becomes full results in actuation of a diaphragm which is arranged to signal the operator or user that a clogged condition exists in the filter bag.
More pertinent to a consideration of the present invention is the automatic shutoff arrangement disclosed in U.S. Pat. No. 3,172,743. Although the vacuum cleaner disclosed therein is not an "upright" in the classic sense, it does embody the well known "clean air" principle by which is meant that the fan in the system does not have to process dirty air but instead is so located that dirt is removed upstream of the fan location by reason of having the filter appropriately located upstream of the fan unit. Moreover, the bag lock-out scheme disclosed in U.S. Pat. No. 3,172,743 does provide both an indication that there is no bag effectively present in the cleaner, and, at the same time, prevents the operation of the fan motor when such a condition exists. Additionally, a pressure differential actuated switch is arranged so as to give a signal to the operator when a "full bag" or clogged filter condition exists within the bag. However, in the vacuum cleaner disclosed in U.S. Pat. No. 3,172,743, such pressure differential switch does not function to interrupt power to the fan motor and thereby prevent the possible damage to the motor assembly caused by the increased thermal load. Further, the pressure differential is sensed between the inlet of the dust bag or filter and the fan and therefore no indication or warning is given should a blockage occur elsewhere in the dirty air passageway of the vacuum system.
Another problem that occurs in the operation of the aforementioned switch which is actuated in response to a predetermined pressure differential is that this differential tends to vary considerably, and in those instances where the switch is designed to shut off the motor, that very action causes reversion of the pressure differential to its original state, thereby allowing the motor to be re-energized.